Lubricant compositions containing ester-substituted hindered phenol antioxidants

ABSTRACT

A composition of an antioxidant of the formula                    
     where R 3  is an alkyl group of 2 to 6 carbon atoms, and a dispersant or a detergent, is a useful additive package for lubricant compositions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of copending application Ser. No.09/761,432 filed Jan. 16, 2001 now U.S. Pat. No. 6,559,105 which claimspriority from Unites States Provisional Application Serial No.60/194,165, filed Apr. 3, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to compositions suitable for use aslubricant additives which contain an ester-substituted hindered phenolantioxidant and other additives suitable for lubricants such as adetergent or a dispersant. The present invention provides an economicalantioxidant which has good performance properties when used in lubricantformulations especially for heavy duty diesel engines and passenger carcrankcase.

U.S. Pat. No. 5,523,007, Kristen et al., Jun. 4, 1996, discloses alubricant oil composition comprising a diesel engine lubricating oiland, as antioxidant, a compound of the formula

X can be —CH₂—CH₂—C(═O)—OR and R is a straight chain or branched alkylradical of the formula —CH_(n)H_(2n+1) wherein n is an integer from 8 to22.

U.S. Pat. No. 3,285,855, Dexter et al., Nov. 15, 1966, disclosesstabilization of organic material with esters containing analkylhydroxyphenyl group. The ester can have the structure

in which x has a value of from 0 to 6, inclusively, and y has a value offrom 6 to 30, inclusively. The “lower alkyl” groups can be t-butyl.Organic materials which can be stabilized include, among many others,lubricating oil of the aliphatic ester type, and mineral oil.

U.S. Pat. No. 5,206,414, Evans et al., Apr. 27, 1993, discloses aprocess for the preparation of compounds of the general formula

A can be —OR₄ where R₄ can be C₂-C₄₅ alkyl.

The present invention provides, among other advantages, a convenientmethod for obtaining a certain class of hindered phenolic esterantioxidants having particularly useful properties. In particular theantioxidants (shown below), that is, those having an R³ group of 2 to 6carbon atoms, can be conveniently prepared in a single step. In apreferred synthesis, no trans-esterification reaction is necessary,resulting in a simplified process which leads to fewer byproducts. Theantioxidants thus prepared impart excellent thermal and oxidativestability to lubricant formulations and show excellent performance inseal durability tests.

SUMMARY OF THE INVENTION

A composition comprising;

(A) at least one antioxidant of the formula

 wherein R³ is an alkyl group containing 2 to 6 carbon atoms; and

(B) at least one component selected from the group consisting ofdispersants and detergents.

DETAILED DESCRIPTION OF THE INVENTION

Various preferred features and embodiments will be described below byway of non-limiting illustration.

Oil of Lubricating Viscosity

Although not required in all embodiments of this invention, commonly anoil of lubricating viscosity is employed as a medium dissolving ordispersing the other components. Oils of lubricating viscosity includenatural and synthetic lubricating oils and mixtures thereof. Theselubricants include crankcase lubricating oils for spark-ignited andcompression-ignited internal combustion engines, including automobileand truck engines, two-cycle engines, aviation piston engines, andmarine and railroad diesel engines. They can also be used in gasengines, stationary power engines, and turbines. Automatic transmissionfluids, transaxle lubricants, gear lubricants, metal-working lubricants,hydraulic fluids and other lubricating oil and grease compositions canalso benefit from the incorporation therein of the compositions of thepresent invention.

Natural oils include animal oils and vegetable oils (e.g., castor oil,lard oil) as well as liquid petroleum oils and solvent-treated oracid-treated mineral lubricating oils of the paraffinic, naphthenic ormixed paraffinic-naphthenic types. Oils of lubricating viscosity derivedfrom coal or shale are also useful base oils. Synthetic lubricating oilsinclude hydrocarbon oils such as polymerized and interpolymerizedolefins (e.g., polybutylenes, polypropylenes, propylene-isobutylenecopolymers, poly(1-hexenes, poly(1-octenes), poly(1-decenes), andmixtures thereof); alkylbenzenes (e.g., dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, and di(2-ethylhexyl)-benzenes);polyphenyls (e.g., biphenyls, terphenyls, and alkylated polyphenyls),alkylated diphenyl ethers and alkylated diphenyl sulfides and thederivatives, analogs, and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof wherethe terminal hydroxyl groups have been modified by esterification,etherification, or similar reaction constitute another class of knownsynthetic lubricating oils. These are exemplified by the oils preparedthrough polymerization of ethylene oxide or propylene oxide, the alkyland aryl ethers of these polyoxyalkylene polymers (e.g.,methylpolyisopropylene glycol ether having an average molecular weightof 1,000 diphenyl ether of polyethylene glycol having a molecular weightof 500-1,000, diethyl ether of polypropylene glycol having a molecularweight of 1,000-1,500) or mono- and polycarboxylic esters thereof, forexample, the acetic acid esters, mixed C₃-C₈ fatty acid esters, or theC₁₃ Oxo acid diester of tetraethylene glycol.

Another suitable class of synthetic lubricating oils comprises theesters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkylsuccinic acids and alkenyl succinic acids, maleic acid, azelaic acid,suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic aciddimer, malonic acid, alkyl malonic acids, and alkenyl malonic acids)with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecylalcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycolmonoether, and propylene glycol). Specific examples of these estersinclude dibutyl adipate, di(2-ethylhexyl sebacate, di-n-hexyl fumarate,dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctylphthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyldiester of linoleic acid dimer, and the complex ester formed by reactingone mole of sebacic acid with two moles of tetraethylene glycol and twomoles of 2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols and polyol ethers such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol, andtripentaerythritol.

Unrefined, refined and rerefined oils (and mixtures of each with eachother) of the type disclosed hereinabove can be used in the lubricantcompositions of the present invention. Unrefined oils are those obtaineddirectly from a natural or synthetic source without further purificationtreatment. For example, a shale oil obtained directly from retortingoperations, a petroleum oil obtained directly from distillation or esteroil obtained directly from an esterification process and used withoutfurther treatment would be an unrefined oil. Refined oils are similar tothe unrefined oils except that they have been further treated in one ormore purification steps to improve one or more properties. Many suchpurification techniques are known to those of skill in the art such asolvent extraction, acid or base extraction, filtration, percolation, orsimilar purification techniques. Rerefined oils are obtained byprocesses similar to those used to obtain refined oils which have beenalready used in service. Such rerefined oils are also known as reclaimedor reprocessed oils and often are additionally processed by techniquesdirected to removal of spent additives and oil breakdown products.

The aliphatic and alicyclic substituents, as well as aryl nuclei, aregenerally described as “hydrocarbon-based”. The meaning of the term“hydrocarbon-based” as used herein is apparent from the followingdetailed discussion of “hydrocarbon-based substituent.”

As used herein, the terms “hydrocarbon-based substituent,” “hydrocarbylsubstituent” or “hydrocarbyl group,” which are used synonymously, areused in their ordinary sense, which is well-known to those skilled inthe art. Specifically, any of these terms refers to a group having acarbon atom directly attached to the remainder of the molecule andhaving predominantly hydrocarbon character. Examples of hydrocarbylgroups include:

(1) hydrocarbon substituents, that is, aliphatic (e.g., alkyl oralkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, andaromatic-, aliphatic-, and alicyclic-substituted aromatic substituents,as well as cyclic substituents wherein the ring is completed throughanother portion of the molecule (e.g., two substituents together form aring);

(2) substituted hydrocarbon substituents, that is, substituentscontaining non-hydrocarbon groups which, in the context of thisinvention, do not alter the predominantly hydrocarbon substituent (e.g.,halo (especially chloro and fluoro), hydroxy, alkoxy, mercapto,alkylmercapto, nitro, nitroso, and sulfoxy);

(3) hetero substituents, that is, substituents which, while having apredominantly hydrocarbon character, in the context of this invention,contain other than carbon in a ring or chain otherwise composed ofcarbon atoms. Heteroatoms include sulfur, oxygen, nitrogen, andencompass substituents as pyridyl, furyl, thienyl and imidazolyl. Ingeneral, no more than two, preferably no more than one, non-hydrocarbonsubstituent will be present for every ten carbon atoms in thehydrocarbyl group; typically, there will be no non-hydrocarbonsubstituents in the hydrocarbyl group.

Preferably, the hydrocarbon-based substituents in the compositions ofthis invention are free from acetylenic unsaturation. Ethylenicunsaturation, when present, preferably will be such that no more thanone ethylenic lineage will be present for every 10 carbon-to-carbonbonds in the substituent. The hydrocarbon-based substituents are usuallyhydrocarbon in nature and more usually, substantially saturatedhydrocarbon. As used in this specification and the appended claims, theword “lower” denotes substituents or groups containing up to sevencarbon atoms; for example, lower alkoxy, lower alkyl, lower alkenyl,lower aliphatic aldehyde.

The amount of lubricating oil in a fully formulated lubricant of thepresent invention (including the diluent or carrier oils present inadditive packages) is typically 80 to 99.5 weight percent, preferably 85to 96 weight percent, and more preferably 90 to 95 weight percent. Thelubricating oil can also be used to prepare concentrates containing theadditives of the present invention in higher concentrations. The amountof such oil in a concentrate is typically 20 to 80 weight percent.

(A) The Antioxidant

The present invention comprises a hindered, ester-substituted phenolsuch as one represented by the formula

and more preferably

In these structures R³ is a straight chain or branched chain alkyl groupcontaining 2 to 6 carbon atoms, preferably 2 to 4, and more preferably 4carbon atoms. R³ is most preferably an n-butyl group.

Hindered, ester-substituted phenols of this type can be prepared byheating a 2,6-dialkylphenol with an acrylate ester under base catalysisconditions, such as aqueous KOH.

EXAMPLE 1

To a 5-L round-bottomed 4-necked flask, equipped with a mechanicalstirrer, thermal probe, and reflux condenser equipped for distillateremoval, is charged 2619 g 2,6-di-t-butylphenol and 17.7 g potassiumhydroxide (technical grade). The reaction mixture is heated to 135° C.over 35 minutes and maintained at temperature for 2 hours, removing 9.7g aqueous distillate. To the reaction mixture is charged 1466 g butylacrylate dropwise over the course of 90 minutes. The temperature ismaintained at 135° C. for up to 2 hours, or until analysis by infraredindicates no further change (by observing peaks at 727 and 768 cm⁻¹). Tothe mixture is charged 103 g magnesium silicate absorbent and 17 gfilter aid and stirring is continued for 2 hours, while removing 7.1 gdistillate. The mixture is filtered through additional filter aid.

The amount of the above antioxidant in a completely formulated lubricantwill typically be 0.05 to 5 percent by weight, preferably 0.25 to 2.0percent by weight, and more preferably 0.3 to 1.5 percent by weight. Itsconcentration in a concentrate will be correspondingly increased, to,e.g., 1 to 75 weight percent.

(B-1) The Dispersant

Dispersants are well known in the field of lubricants and includeprimarily what are sometimes referred to as “ashless” dispersantsbecause (prior to mixing in a lubricating composition) they do notcontain ash-forming metals and they do not normally contribute any ashforming metals when added to a lubricant. Dispersants are characterizedby a polar group attached to a relatively high molecular weighthydrocarbon chain.

One class of dispersant is Mannich bases. These are materials which areformed by the condensation of a higher molecular weight, alkylsubstituted phenol, an alkylene polyamine, and an aldehyde such asformaldehyde. Such materials may have the general structure

(including a variety of isomers and the like) and are described in moredetail in U.S. Pat. No. 3,634,515.

Another class of dispersant is high molecular weight esters. Thesematerials are similar to the above-described Mannich dispersants or thesuccinimides described below, except that they may be seen as havingbeen prepared by reaction of a hydrocarbyl acylating agent and apolyhydric aliphatic alcohol such as glycerol, pentaerythritol, orsorbitol. Such materials are described in more detail in U.S. Pat. No.3,381,022.

Other dispersants include polymeric dispersant additives, which aregenerally hydrocarbon-based polymers which contain polar functionalityto impart dispersancy characteristics to the polymer.

A preferred class of dispersants is the carboxylic dispersants.Carboxylic dispersants include succinic-based dispersants, which are thereaction product of a hydrocarbyl substituted succinic acylating agentwith an organic hydroxy compound or, preferably, an amine containing atleast one hydrogen attached to a nitrogen atom, or a mixture of saidhydroxy compound and amine. The term “succinic acylating agent” refersto a hydrocarbon-substituted succinic acid or succinic acid-producingcompound (which term also encompasses the acid itself). Such materialstypically include hydrocarbyl-substituted succinic acids, anhydrides,esters (including half esters) and halides.

Succinic based dispersants have a wide variety of chemical structuresincluding typically structures such as

In the above structure, each R¹ is independently a hydrocarbyl group,preferably a polyolefin-derived group having an {overscore (M)}_(n) of500 or 700 to 10,000. Typically the hydrocarbyl group is an alkyl group,frequently a polyisobutyl group with a molecular weight of 500 or 700 to5000, preferably 1500 or 2000 to 5000. Alternatively expressed, the R¹groups can contain 40 to 500 carbon atoms and preferably at least 50,e.g., 50 to 300 carbon atoms, preferably aliphatic carbon atoms. The R²are alkenyl groups, commonly ethylenyl (C₂H₄) groups. Such molecules arecommonly derived from reaction of an alkenyl acylating agent with apolyamine, and a wide variety of linkages between the two moieties ispossible beside the simple imide structure shown above, including avariety of amides and quaternary ammonium salts. Succinimide dispersantsare more fully described in U.S. Pat. Nos. 4,234,435 and 3,172,892.

The polyalkenes from which the substituent groups are derived aretypically homopolymers and interpolymers of polymerizable olefinmonomers of 2 to 16 carbon atoms; usually 2 to 6 carbon atoms.

The olefin monomers from which the polyalkenes are derived arepolymerizable olefin monomers characterized by the presence of one ormore ethylenically unsaturated groups (i.e., >C═C<); that is, they aremono-olefinic monomers such as ethylene, propylene, 1-butene, isobutene,and 1-octene or polyolefinic monomers (usually diolefinic monomers) suchas 1,3-butadiene, and isoprene. These olefin monomers are usuallypolymerizable terminal olefins; that is, olefins characterized by thepresence in their structure of the group >C═CH₂. Relatively smallamounts of non-hydrocarbon substituents can be included in thepolyolefin, provided that such substituents do not substantiallyinterfere with formation of the substituted succinic acid acylatingagents.

Each R¹ group may contain one or more reactive groups, e.g., succinicgroups, thus being represented (prior to reaction with the amine) bystructures such as

in which y represents the number of such succinic groups attached to theR¹ group. In one type of dispersant, y=1. In another type of dispersant,y is greater than 1, preferably greater than 1.3 or greater than 1.4;and most preferably y is equal to or greater than 1.5. Preferably y is1.4 to 3.5, especially is 1.5 to 3.5 and most especially 1.5 to 2.5.Fractional values of y, of course, can arise because different specificR¹ chains may be reacted with different numbers of succinic groups.

The amines which are reacted with the succinic acylating agents to formthe carboxylic dispersant composition can be monoamines or polyamines.In either case they will be characterized by the formula R⁴R⁵NH whereinR⁴ and R⁵ are each independently hydrogen, or hydrocarbon,amino-substituted hydrocarbon, hydroxy-substituted hydrocarbon,alkoxy-substituted hydrocarbon, amino, carbamyl, thiocarbamyl, guanyl,and acylimidoyl groups provided that only one of R⁴ and R⁵ is hydrogen.In all cases, therefore, they will be characterized by the presencewithin their structure of at least one H—N<group. Therefore, they haveat least one primary (i.e., H₂N—) or secondary amino (i.e., H—N<) group.Examples of monoamines include ethylamine, diethylamine, n-butylamine,di-n-butylamine, allylamine, isobutylamine, cocoamine, stearylamine,laurylamine, methyllaurylamine, oleyl-amine, N-methyl-octylamine,dodecylamine, and octadecylamine.

The polyamines from which (C) is derived include principally alkyleneamines conforming, for the most part, to the formula

wherein t is an integer preferably less than 10, A is a hydrogen groupor a hydrocarbyl group preferably having up to 30 carbon atoms, and thealkylene group is preferably an alkylene group having less than 8 carbonatoms. The alkylene amines include principally methylene amines,ethylene amines, hexylene amines, heptylene amines, octylene amines,other polymethylene amines. They are exemplified specifically by:ethylene diamine, triethylene tetramine, propylene diamine,decamethylene diamine, octamethylene diamine, di(heptamethylene)triamine, tripropylene tetramine, tetraethylene pentamine, trimethylenediamine, pentaethylene hexamine, di(-trimethylene) triamine. Higherhomologues such as are obtained by condensing two or more of theabove-illustrated alkylene amines likewise are useful. Tetraethylenepentamines is particularly useful.

The ethylene amines, also referred to as polyethylene polyamines, areespecially useful. They are described in some detail under the heading“Ethylene Amines” in Encyclopedia of Chemical Technology, Kirk andOthmer, Vol. 5, pp. 898-905, Interscience Publishers, New York (1950).

Hydroxyalkyl-substituted alkylene amines, i.e., alkylene amines havingone or more hydroxyalkyl substituents on the nitrogen atoms, likewiseare useful. Examples of such amines include N-(2-hydroxyethyl)ethylenediamine, N,N′-bis(2-hydroxy-ethyl)-ethylene diamine,1-(2-hydroxyethyl)piperazine, mono-hydroxypropyl)-piperazine,di-hydroxypropy-substituted tetraethylene pentamine,N-(3-hydroxypropyl)-tetra-methylene diamine, and2-heptadecyl-1-(2-hydroxyethyl)-imidazoline.

Higher homologues, such as are obtained by condensation of theabove-illustrated alkylene amines or hydroxy alkyl-substituted alkyleneamines through amino radicals or through hydroxy radicals, are likewiseuseful.

The carboxylic dispersant composition (C), obtained by reaction of thesuccinic acid-producing compounds and the amines described above, may beamine salts, amides, imides, imidazolines as well as mixtures thereof.To prepare the carboxylic dispersant composition (C), one or more of thesuccinic acid-producing compounds and one or more of the amines areheated, optionally in the presence of a normally liquid, substantiallyinert organic liquid solvent/diluent at an elevated temperature,generally in the range of 80° C. up to the decomposition point of themixture or the product; typically 100° C. to 300° C.

The succinic acylating agent and the amine (or organic hydroxy compound,or mixture thereof) are typically reacted in amounts sufficient toprovide at least one-half equivalent, per equivalent of acid-producingcompound, of the amine (or hydroxy compound, as the case may be).Generally, the maximum amount of amine present will be about 2 moles ofamine per equivalent of succinic acylating agent. For the purposes ofthis invention, an equivalent of the amine is that amount of the aminecorresponding to the total weight of amine divided by the total numberof nitrogen atoms present. The number of equivalents of succinicacid-producing compound will vary with the number of succinic groupspresent therein, and generally, there are two equivalents of acylatingreagent for each succinic group in the acylating reagents. Additionaldetails and examples of the procedures for preparing thenitrogen-containing compositions of the present invention by reaction ofsuccinic acid-producing compounds and amines are included in, forexample, U.S. Pat. Nos. 3,172,892; 3,219,666; 3,272,746; and 4,234,435.

The dispersants may be borated materials. Borated dispersants arewell-known materials and can be prepared by treatment with a boratingagent such as boric acid. Typical conditions include heating thedispersant with boric acid at 100 to 150° C. The dispersants may also betreated by reaction with maleic anhydride as described in PCTapplication US99/23940 filed Oct. 13, 1999.

The amount of the dispersant in a completely formulated lubricant, ifpresent, will typically be 0.5 to 10 percent by weight, preferably 1 to8 percent by weight, and more preferably 3 to 7 percent by weight. Itsconcentration in a concentrate will be correspondingly increased, to,e.g., 5 to 80 weight percent.

(B-2) The Detergent

Detergents are generally salts of organic acids, which are oftenoverbased. Metal overbased salts of organic acids are widely known tothose of skill in the art and generally include metal salts wherein theamount of metal present exceeds the stoichiometric amount. Such saltsare said to have conversion levels in excess of 100% (i.e., theycomprise more than 100% of the theoretical amount of metal needed toconvert the acid to its “normal” or “neutral” salt). They are commonlyreferred to as overbased, hyperbased or superbased salts and are usuallysalts of organic sulfur acids, organic phosphorus acids, carboxylicacids, phenols or mixtures of two or more of any of these. As-a skilledworker would realize, mixtures of such overbased salts can also be used.

The terminology “metal ratio” is used in the prior art and herein todesignate the ratio of the total chemical equivalents of the metal inthe overbased salt to the chemical equivalents of the metal in the saltwhich would be expected to result in the reaction between the organicacid to be overbased and the basic reacting metal compound according tothe known chemical reactivity and stoichiometry of the two reactants.Thus, in a normal or neutral salt the metal ratio is one and, in anoverbased salt, the metal ratio is greater than one. The over basedsalts used as component (A) in this invention usually have metal ratiosof at least 3:1. Typically, they have ratios of at least 12:1. Usuallythey have metal ratios not exceeding 40:1. Typically, salts havingratios of 12:1 to 20:1 are used.

Overbased compositions are well known, and the general process forpreparing overbased compositions is described in connection with thepreparation of overbased Mg saligenin derivatives, below. The optionalother overbased compositions can be prepared based on a variety of otherwell known organic acidic materials including sulfonic acids, carboxylicacids (including substituted salicylic acids), phenols, phosphonicacids, and mixtures of any two or more of these. These materials andmethods for overbasing of them are well known from numerous U.S. Patentsincluding those mentioned above in connection with the overbasing of thesaligenin derivative and need not be further described in detail.

Preferred overbased materials include overbased phenates derived fromthe reaction of an alkylated phenol, preferably wherein the alkyl grouphas at least 6 aliphatic carbon atoms. The phenate is optionally reactedwith formaldehyde or a sulfurization agent, or mixtures thereof, toprovide a bridged or linked structure.

Other preferred overbased materials include metal overbased sulfonatesderived from an alkylated aryl sulfonic acid wherein the alkyl group hasat least about 15 aliphatic carbon atoms.

Other preferred overbased materials include metal overbased carboxylatesderived from fatty acids having at least about 8 aliphatic carbon atoms.

The basically reacting metal compounds used to make these overbasedsalts are usually an alkali or alkaline earth metal compound (i.e., theGroup IA, IIA, and IIB metals excluding francium and radium andtypically excluding rubidium, cesium and beryllium), although otherbasically reacting metal compounds can be used. Compounds of Ca, Ba, Mg,Na and Li, such as their hydroxides and alkoxides of lower alkanols areusually used as basic metal compounds in preparing these overbased saltsbut others can be used as shown by the prior art referred to herein.Overbased salts containing a mixture of ions of two or more of thesemetals can be used in the present invention.

Overbased materials are generally prepared by reacting an acidicmaterial (typically an inorganic acid or lower carboxylic acid,preferably carbon dioxide) with a mixture comprising an acidic organiccompound, a reaction medium comprising at least one inert, organicsolvent (mineral oil, naphtha, toluene, xylene, etc.) for said acidicorganic material, a stoichiometric excess of a metal base, and apromoter. The acidic organic compound will, in the present instance, bethe above-described saligenin derivative.

The acidic material used in preparing the overbased material can be aliquid such as formic acid, acetic acid, nitric acid, or sulfuric acid.Acetic acid is particularly useful. Inorganic acidic materials can alsobe used, such as HCl, SO₂, SO₃, CO₂, or H₂S, preferably CO₂ or mixturesthereof, e.g., mixtures of CO₂ and acetic acid.

A promoter is a chemical employed to facilitate the incorporation ofmetal into the basic metal compositions. The promoters are diverse andare well known in the art. A discussion of suitable promoters is foundin U.S. Pat. Nos. 2,777,874, 2,695,910, and 2,616,904. These include thealcoholic and phenolic promoters, which are preferred. The alcoholicpromoters include the alkanols of one to twelve carbon atoms such asmethanol, ethanol, amyl alcohol, octanol, isopropanol, and mixtures ofthese. Phenolic promoters include a variety of hydroxy-substitutedbenzenes and naphthalenes, a particularly useful class of phenols arethe alkylated phenols of the type listed in U.S. Pat. No. 2,777,874,e.g., heptylphenols, octylphenols, and nonylphenols. Mixtures of variouspromoters are sometimes used.

Patents specifically describing techniques for making basic salts ofacidic organic compounds generally include U.S. Pat. Nos. 2,501,731;2,616,905; 2,616,911; 2,616,925; 2,777,874; 3,256,186; 3,384,585;3,365,396; 3,320,162; 3,318,809; 3,488,284; and 3,629,109.

One useful detergent compound is a metal saligenin derivative. Suchmaterials have been described in detail in U.S. Provisional ApplicationNo. 60/194,136. When the metal is magnesium, the compound is representedby the formula

That is, it is a metal salt, and preferably a magnesium salt. In thisstructure, (Mg) represents a valence of a magnesium ion. (Other valencesof the normally divalent Mg ion, not shown, can be satisfied by otheranions or by association with additional —O⁻ functionality of the sameor additional saligenin derivatives.) Each n is independently 0 or 1,provided that when n is 0, the Mg is replaced by H, that is, to form anunneutralized phenolic —OH group. The average value of n in thecomposition overall is typically 0.1 to 1.0. That is, the structurerepresents a partially or completely neutralized magnesium salt, a valueof 1.0 corresponding to complete neutralization of each site by thedivalent Mg ion. The compound contains one aromatic ring or amultiplicity of aromatic rings linked by “Y” groups, and also “X”groups. The value of “m” can be 0 to 10, which means that the number ofsuch rings will be 1 to 11, although it is to be understood that theupper limit of “m” is not a critical variable. Preferably m is 2 to 9,more preferably 3 to 8 or 4 to 6. It is also permitted that one of the Xgroups can be —H, particularly if m is 1 or greater. Other suitablemetals include alkali metals such as lithium, sodium, or potassium;alkaline earth metals such as calcium or barium; and other metals suchas copper, zinc, and tin, and mixtures of such metals.

Most of the rings contain at least one R¹ substituent, which is ahydrocarbyl group, preferably an alkyl group, containing 1 to 60 carbonatoms, preferably 7 to 28 carbon atoms, more preferably 9 to 18 carbonatoms. Of course it is understood that R¹ will normally comprise amixture of various chain lengths, so that the foregoing numbers willnormally represent an average number of carbon atoms in the R¹ groups(number average). Each ring in the structure will be substituted with 0,1, 2, or 3 such R¹ groups (that is, p is 0, 1, 2, or 3), most typically1, and of course different rings in a given molecule may containdifferent numbers of such substituents. At least one aromatic ring inthe molecule must contain at least one R¹ group, and the total number ofcarbon atoms in all the R¹ groups in the molecule should be at least 7,preferably at least 12.

In the above structure the X and Y groups may be seen as groups derivedfrom formaldehyde or a formaldehyde source, by condensative reactionwith the aromatic molecule. The relative amounts of the various X and Ygroups depends to a certain extent on the conditions of synthesis of themolecules. While various species of X and Y may be present in themolecules in question, the commonest species comprising X are —CHO(aldehyde functionality) and —CH₂OH (hydroxymethyl functionality);similarly the commonest species comprising Y are —CH₂— (methylenebridge) and —CH₂OCH₂— (ether bridge). The relative molar amounts ofthese species in a sample of the above material can be determined by¹H/¹³C NMR as each carbon and hydrogen nucleus has a distinctiveenvironment and produces a distinctive signal. (The signal for the etherlinkage, —CH₂OCH₂— must be corrected for the presence of two carbonatoms, in order to arrive at a correct calculation of the molar amountof this material. Such a correction is well within the abilities of theperson skilled in the art.)

In a preferred embodiment, X is at least in part —CHO and such —CHOgroups comprise at least 10, 12, or 15 mole percent of the X and Ygroups. Preferably the —CHO groups comprise 20 to 60 mole percent of theX and Y groups and more preferably 25 to 40 mole percent of the X and Ygroups.

In another embodiment, X is at least in part —CH₂OH and such —CH₂OHgroups comprise 10 to 50 mole percent of the X and Y groups, preferably15 to 30 mole percent of the X and Y groups.

In an embodiment in which m is non-zero, Y is at least in part —CH₂— andsuch —CH₂— groups comprise 25 to 55 mole percent of the X and Y groups,preferably 32 to 45 mole percent of the X and Y groups.

In another embodiment Y is at least in part —CH₂OCH₂— and such —CH₂OCH₂—groups comprise 5 to 20 mole percent of the X and Y groups, andpreferably 10 to 16 mole percent of the X and Y groups.

The above-described compound is preferably a magnesium salt and, indeed,the presence of magnesium during the preparation of the condensedproduct is believed to be important in achieving the desired ratios of Xand Y components described above. The number of Mg ions in thecomposition is characterized by an average value of “n” of 0.1 to 1.0,preferably 0.2 or 0.4 to 0.9, and more preferably 0.6 to 0.8, whichcorrespond to 20-100%, 20 or 40-90%, or 60-80% neutralization by Mg.Since Mg is normally a divalent ion, it can neutralize up to twophenolic hydroxy groups. Those two hydroxy groups may be on the same oron different molecules. If the value of n is less than 1.0, thisindicates that the hydroxy groups are less than completely neutralizedby Mg ions. Alternatively, each Mg ion could be associated with onephenolic anion and an ion of another type such as a hydroxy (OH⁻) ion orcarbonate ion (CO₃ ⁻), while still providing an n value of 1.0. Thespecification that the average value of n is 0.1 to 1.0 is not directlyapplicable to overbased versions of this material (described below andalso a part of the present invention) in which an excess of Mg oranother cation can be present. It should be understood that, even in anoverbased material, some fraction of the phenolic OH groups may not havereacted with the magnesium and may retain the OH structure.

It is understood that in a sample of a large number of molecules, someindividual molecules will exist which deviate from these parameters: forinstance, there may be some molecules containing no R¹ groupswhatsoever. Likewise, some fraction of molecules may contain only one(or even zero) X groups, while some may contain more than two X groups.And some fraction of the aromatic groups may be linked by Y groups tomore than two neighboring aromatic groups. These molecules could beconsidered as impurities, and their presence will not negate the presentinvention so long as the majority (and preferably the substantialmajority) of the molecules of the composition are as described. In anyevent, compositions exhibiting this type of variability are to beconstrued as encompassed by the present invention and the descriptionthat a material is “represented by” the formula shown. There is believedto be a reasonable possibility that a significant fraction of thepolynuclear molecules of the present invention may bear only a single Xgroup. In order to explicitly account for this possibility, it is to beunderstood that in the materials of an embodiment of the presentinvention, especially if m is 1 or greater, one (but preferably notboth) of the X groups in the above structures can be —H.

The above-described component can be prepared by combining a phenolsubstituted by the above-described R¹ group with formaldehyde or asource of formaldehyde and magnesium oxide or magnesium hydroxide underreactive conditions, in the presence of a catalytic amount of a strongbase. Common reactive equivalents of formaldehyde includesparaformaldehyde, paraldehyde, trixoane, formalin and methal. Forconvenience, paraformaldehyde is preferred.

The relative molar amounts of the substituted phenol and theformaldehyde can be important in providing products with the desiredstructure and properties. It is preferred that the substituted phenoland formaldehyde are reacted in equivalent ratios of 1:1 to 1:3 or 1.4,more preferably 1:1.1 to 1:2.9 or 1:1.4 to 1:2.6, and still morepreferably 1:1.7 to 1:2.3. Thus under preferred conditions there will beabout a 2:1 equivalent excess of formaldehyde. (One equivalent offormaldehyde is considered to correspond to one H₂CO unit; oneequivalent of phenol is considered to be one mole of phenol.)

The strong base is preferably sodium hydroxide or potassium hydroxide,and can be supplied in an aqueous solution.

The process can be conducted by combining the above components with anappropriate amount of magnesium oxide or magnesium hydroxide withheating and stirring. A diluent such as mineral oil or other diluent oilcan be included to provide for suitable mobility of the components. Anadditional solvent such as an alcohol can be included if desired,although it is believed that the reaction may proceed more efficientlyin the absence of additional solvent. The reaction can be conducted atroom temperature or, preferably, a slightly elevated temperature such as35-120° C., 70-110° C., or 90-100° C., and of course the temperature canbe increased in stages. When water is present in the reaction mixture itis convenient to maintain the mixture at or below the normal boilingpoint of water. After reaction for a suitable time (e.g., 30 minutes to5 hours or 1 to 3 hours) the mixture can be heated to a highertemperature, preferably under reduced pressure, to strip off volatilematerials. Favorable results are obtained when the final temperature ofthis stripping step is 100 to about 150° C., preferably 120 to about145° C.

Reaction under the preferred conditions described above leads to aproduct which has a relatively high content of —CHO substituent groups,that is, 10%, 12%, and preferably 15% and greater. Such materials, whenused as detergents in lubricating compositions, exhibit good upperpiston cleanliness performance, low Cu/Pb corrosion, and goodcompatibility with seals. Use of metals other than magnesium in thesynthesis typically leads to a reduction in the content of —CHOsubstituent groups.

EXAMPLE 2

To a 5-L, 4-necked round bottom flask equipped with stirrer, stopper,thermowell, and reflux condenser, the following are charged: 670 gdiluent oil (mineral oil), 1000 g dodecyl phenol, and a solution of 3 gNaOH in 40 g water. The mixture is heated to 35° C. with stirring (350r.p.m.). When 35° C. is attained, 252 g of paraformaldehyde (90%) areadded to the mixture and stirring is continued. After 5 minutes, 5 g ofMgO and 102 g of additional diluent oil are added. The mixture is heatedto 79° C. and held at temperature for 30 minutes. A second increment of58 g MgO is added and the batch further heated and maintained at 95-100°C. for 1 hour. Thereafter the mixture is heated to 120° C. under a flowof nitrogen at 28 L/hr (1.0 std. ft³/hr.). When 120° C. is reached, 252g diluent oil is added, and the mixtures is stripped for 1 hour at apressure of 2.7 kPa (20 torr) at 120° C. for 1 hour and then filtered.

The resulting product is analyzed and contains 1.5% by weight magnesiumand has a Total Base Number (TBN) of 63. Analysis of the product by IDand 2D ¹H/¹³C NMR reveals an aldehyde content of 29 mole %, a methylenebridge content of 38 mole %, an ether bridge content of 12 mole %, and ahydroxymethyl content of 21 mole %.

The material prepared by the above process can be further treated byboration or by overbasing. Borated compositions are prepared by reactionof the above-described saligenin derivative one or more boron compounds.Suitable boron compounds include boric acid, borate esters, and alkalior mixed alkali metal and alkaline earth metal borates. These metalborates are generally a hydrated particulate metal borate and they, aswell as the other borating agents, are known in the art and areavailable commercially. Typically the saligenin derivative is heatedwith boric acid at 50-100° C.

The material can also be overbased. Overbased salts of organic acidsgenerally, and methods of their synthesis, have been described above andare widely known to those of skill in the art. The magnesium saligeninderivative can be overbased using additional Mg metal or using adifferent metal.

EXAMPLE 3 Mg Saligenin Derivative Overbased with Ca

Into a 2 L four-necked flask equipped with stirrer, thermowell, refluxcondenser, and a subsurface tube, is charged 1000 g of the product ofExample 2 (Mg saligenin derivative in diluent oil), 50 g of a mixture ofisobutyl and amyl alcohols, 100 g of methanol, and 74 g of Ca(OH)₂. Asolution of 1 g acetic acid in 4 g water is added to the flask and thecontents are held, with stirring, at 44° C. for 30 minutes. Carbondioxide is blown through the mixture for 1 hour or longer, at 14 L/hr(0.5 std. ft³/hr.) until a direct base number of 15 is obtained. Themixture is heated to 120° C. under a nitrogen flow of 28 L/hr (1.0 std.ft³/hr.) for 1 hour, to strip volatiles. The resulting mixture isfiltered and determined to have a TBN of 142 and to contain 3% Ca and1.4% Mg by weight. NMR analysis reveals 30% aldehyde functionality, 39%methylene coupling, 17% ether coupling, and 14% hydroxymethylfunctionality.

EXAMPLE 4 Mg Overbased Saligenin Derivative

Into a 2-liter, four-necked flask equipped with stirrer, thermowell,reflux condenser, and subsurface tube, is charged 1000 g of the productof example 2, 50 g of a mixture of isobutyl and amyl alcohols, and 63 gMgO. The mixture is heated, with stirring, to 50° C. A solution of 130 gof stearic acid and 100 g of dil oil is added. The mixture is heated to70° C. and held at this temperature for 3 hours. The mixture was cooledto 60° C. To the mixture, 100 g of methanol and 7 g acetic acid areadded. Carbon dioxide is blown through the mixture for over 3 hours at28 L/hr (0.5 std. ft³/hr) until a direct base number of less than 5 isobtained for the mixture. The mixture is stripped to 120° C. under acarbon dioxide flow of 28 L/hr (0.5 std. ft³/hr) and held at thistemperature for 1 hour under nitrogen flow at 14 L/hr (0.5 std. ft³/hr).The product is filtered and determined to have a TBN of 130 and tocontain 2.8 weight % magnesium. Analysis reveals 32% aldehydefunctionality, 41% methylene coupling, 12% ether coupling, and 15%hydroxymethyl functionality.

The detergents generally can also be borated by treatment with aborating agent such as boric acid. Typical conditions include heatingthe detergent with boric acid at 100 to 150° C., the number ofequivalents of boric acid being roughly equal to the number ofequivalents of metal in the salt. U.S. Pat. No. 3,929,650 disclosesborated complexes and their preparation.

The amount of the detergent component in a completely formulatedlubricant, if present, will typically be 0.5 to 10 percent by weight,preferably 1 to 7 percent by weight, and more preferably 1.2 to 4percent by weight. Its concentration in a concentrate will becorrespondingly increased, to, e.g., 5 to 65 weight percent.

(C) The Metal Salt of a Phosphorus Acid

Metal salts of the formula

wherein R⁸ and R⁹ are independently hydrocarbyl groups containing 3 to30 carbon atoms are readily obtainable by the reaction of phosphoruspentasulfide (P₂S₃) and an alcohol or phenol to form anO,O-dihydrocarbyl phosphorodithioic acid corresponding to the formula

The reaction involves mixing at a temperature of 20° C. to 200° C., fourmoles of an alcohol or a phenol with one mole of phosphoruspentasulfide. Hydrogen sulfide is liberated in this reaction. The acidis then reacted with a basic metal compound to form the salt. The metalM, having a valence n, generally is aluminum, lead, tin, manganese,cobalt, nickel, zinc, or copper, and most preferably zinc. The basicmetal compound is thus preferably zinc oxide, and the resulting metalcompound is represented by the formula

The R⁸ and R⁹ groups are independently hydrocarbyl groups that arepreferably free from acetylenic and usually also from ethylenicunsaturation. They are typically alkyl, cycloalkyl, aralkyl or alkarylgroup and have 3 to 20 carbon atoms, preferably 3 to 16 carbon atoms andmost preferably up to 13 carbon atoms, e.g., 3 to 12 carbon atoms. Thealcohols which react to provide the R⁸ and R⁹ groups can be one or moreprimary alcohols, one or more secondary alcohols, a mixture of secondaryalcohol and primary alcohol. A mixture of two secondary alcohols such asisopropanol and 4-methyl-2-pentanol is often desirable.

Such materials are often referred to as zinc dialkyldithiophosphates orsimply zinc dithiophosphates. They are well known and readily availableto those skilled in the art of lubricant formulation.

The amount of the metal salt of a phosphorus acid in a completelyformulated lubricant, if present, will typically be 0.1 to 5 percent byweight, preferably 0.3 to 2 percent by weight, and more preferably 0.5to 1.5 percent by weight. Its concentration in a concentrate will becorrespondingly increased, to, e.g., 5 to 60 weight percent.

EXAMPLE 5 Fully Formulated Lubricant

A fully formulated lubricant is prepared in a mineral oil base fluid(containing viscosity modifier). The lubricant contains, in addition to1.0 percent by weight (active chemical) of the phenolic antioxidant ofExample 1, the following additional components: a polyolefin amidealkeneamine dispersant, 3.6%; zinc alkyl dithiophosphate, 1.1%;overbased sulfonate detergent(s), 1.6%; overbased phenate detergent(s)1.5%, and 100 p.p.m. polydimethylsiloxane antifoam agent. The lubricanthas a total base number of 10.1 and contains 1.4% sulfated ash.

EXAMPLE 6 Fully Formulated Lubricant

A fully formulated lubricant is prepared in a mineral oil base fluid(containing viscosity modifier). The lubricant contains, in addition to1.0 percent by weight (active chemical) of the phenolic antioxidant ofExample 1, the following additional components: 0.5% of an alkenyl estersulfide inhibitor, a polyolefin amide alkeneamine dispersant, 3.6%;polyolefin anhydride, 0.3%; zinc alkyl dithiophosphate, 1.1%; overbasedsulfonate detergent(s), 1.8%; overbased phenate detergent(s) 1.3%, and100 p.p.m. polydimethylsiloxane antifoam agent. The lubricant has atotal base number of 11.1 and contains 1.5% sulfated ash.

EXAMPLE 7

As an illustration of the effectiveness of the present antioxidant inminimizing deposit formation, a hot tube test was performed. This testcompares a sample of lubricant containing the presently claimedantioxidant (where the R³ alkyl group contains 4 carbon atoms) with alubricant containing an antioxidant in which the R³ group contains 8carbon atoms. The hot tube test simulates deposit-forming tendencies incrankcase lubricants. A sample of lubricant is fed continuously alongwith air through a small glass tube at elevated temperatures for 16hours. At the conclusion of the test the deposits on the tube arevisually rated. Higher ratings indicate less deposits (greater thermalstability). A rating of 7.0 or greater on a scale of 10 is consideredacceptable. Although at high concentrations (1.0 or 1.5 percent byweight of the antioxidant) both samples provide ratings of 7.5 (or inone run 8.0), at the more critical, lower concentration of 0.5 percent,the material of the present invention exhibits improved performance.

Test Samples: Both samples contain about 53 parts of a 145 N oil andabout 24 parts of a 600 N oil; 14.3 parts of commercial heavy dutydiesel and other additive(s); 7.2 parts of a viscosity improver; and 1.1parts of an overbased calcium sulfonate detergent (all the foregoingamounts uncorrected for the presence of conventional diluent oil).Formulation A (inventive) contains in addition 0.5% of the C₄ alkylester of 3-(4-hydroxy-3,5-di-t-butylphenyl)propanoic acid. Formulation B(comparative) contains 0.5% of the C₈ alkyl ester of3-(4-hydroxy-3,5-di-t-butylphenyl)-propanoic acid.

The test results are shown in the following table:

Formulation A B (comparative) Rating at 280° C. 7.5 6.5 Rating at 290°C. 7.5 4.5

The compositions of the present invention may also include, or exclude,conventional amounts of other components which are commonly found inlubricating compositions. For instance, corrosion inhibitors, extremepressure agents, and anti-wear agents include but are not limited todithiophosphoric esters; chlorinated aliphatic hydrocarbons;boron-containing compounds including borate esters; and molybdenumcompounds. Viscosity improvers include but are not limited topolyisobutenes, polymethyacrylate acid esters, polyacrylate acid esters,diene polymers, polyalkyl styrenes, alkenyl aryl conjugated dienecopolymers, polyolefins and multifunctional viscosity improvers. Pourpoint depressants are a particularly useful type of additive, oftenincluded in the lubricating oils described herein usually comprisingsubstances such as polymethacrylates, styrene-based polymers,crosslinked alkyl phenols, or alkyl naphthalenes. See for example, page8 of “Lubricant Additives” by C. V. Smalheer and R. Kennedy Smith(Lesius-Hiles Company Publishers, Cleveland, Ohio, 1967). Anti-foamagents used to reduce or prevent the formation of stable foam includesilicones or organic polymers. Examples of these and additionalanti-foam compositions are described in “Foam Control Agents”, by HenryT. Kerner (Noyes Data Corporation, 1976), pages 125-162. Additionalantioxidants can also be included, typically of the aromatic amine orhindered phenol type. These and other additives which may be used incombination with the present invention are described in greater detailin U.S. Pat. No. 4,582,618 (column 14, line 52 through column 17, line16, inclusive).

Each of the documents referred to above is incorporated herein byreference. Except in the Examples, or where otherwise explicitlyindicated, all numerical quantities in this description specifyingamounts of materials, reaction conditions, molecular weights, number ofcarbon atoms, and the like, are to be understood as modified by the word“about.” Unless otherwise indicated, each chemical or compositionreferred to herein should be interpreted as being a commercial gradematerial which may contain the isomers, by-products, derivatives, andother such materials which are normally understood to be present in thecommercial grade. However, the amount of each chemical component ispresented exclusive of any solvent or diluent oil which may becustomarily present in the commercial material, unless otherwiseindicated. It is to be understood that the upper and lower amount,range, and ratio limits set forth herein may be independently combined.As used herein, the expression “consisting essentially of” permits theinclusion of substances which do not materially affect the basic andnovel characteristics of the composition under consideration.

What is claimed is:
 1. A process for preparing a hindered,ester-substituted phenol, comprising the steps of: (a) heating a2,6-dialkylphenol with an acrylate ester under base catalysisconditions; (b) thereafter adding magnesium silicate absorbent to thereaction mixture; and (c) filtering the resulting mixture.
 2. Theprocess of claim 1 wherein the base is potassium hydroxide.
 3. Theprocess of claim 1 wherein the 2,6-dialkylphenol is di-t-butylphenol. 4.The process of claim 1 wherein the 2,6-dialkylphenol is2,6-di-t-butylphenol and the base is potassium hydroxide, and whereinthe 2,6-di-t-butylphenol and the potassium hydroxide are mixed andheated to about 135° C. over about 35 minutes and maintained at thattemperature for about 2 hours.
 5. The process of claim 1 wherein theacrylate ester is butyl acrylate.
 6. The process of claim 5 wherein thebutyl acrylate is charged to the reaction mixture drop wise over thecourse of about 90 minutes.
 7. The process of claim 6 wherein after theaddition of the butyl acrylate, the temperature of the reaction mixtureis maintained at about 135° C. for up to about 2 hours, or untilanalysis by infrared indicates no further change by observing peaks at727 and 768 cm⁻¹.
 8. The process of claim 1 wherein the magnesiumsilicate is stirred with the reaction mixture prior to filtration. 9.The process of claim 1 wherein the mixture is filtered using a filteraid.